How do you 'realloc' in C++?

Question

How can I realloc in C++? It seems to be missing from the language - there is new and delete but not resize!

I need it because as my program reads more data, I need to reallocate the buffer to hold it. I don't think deleteing the old pointer and newing a new, bigger one, is the right option.

Answer 1

Use ::std::vector!

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Type* t = (Type*)malloc(sizeof(Type)*n)  memset(t, 0, sizeof(Type)*m) 

becomes

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::std::vector<Type> t(n, 0); 

Then

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t = (Type*)realloc(t, sizeof(Type) * n2); 

becomes

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t.resize(n2); 

If you want to pass pointer into function, instead of

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Foo(t) 

use

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Foo(&t[0]) 

It is absolutely correct C++ code, because vector is a smart C-array.

Answer 2

The right option is probably to use a container that does the work for you, like std::vector.

new and delete cannot resize, because they allocate just enough memory to hold an object of the given type. The size of a given type will never change. There are new[] and delete[] but there's hardly ever a reason to use them.

What realloc does in C is likely to be just a malloc, memcpy and free, anyway, although memory managers are allowed to do something clever if there is enough contiguous free memory available.